U.S. patent number 7,820,300 [Application Number 11/156,425] was granted by the patent office on 2010-10-26 for article of manufacture and process for anodically coating an aluminum substrate with ceramic oxides prior to organic or inorganic coating.
This patent grant is currently assigned to Henkel AG & Co. KGaA. Invention is credited to Shawn E. Dolan.
United States Patent |
7,820,300 |
Dolan |
October 26, 2010 |
Article of manufacture and process for anodically coating an
aluminum substrate with ceramic oxides prior to organic or
inorganic coating
Abstract
An article of manufacture and a process for making the article
by the anodization of aluminum and aluminum alloy workpieces to
provide corrosion-, heat- and abrasion-resistant ceramic coatings
comprising titanium and/or zirconium oxides, and the subsequent
coating of the anodized workpiece with a second coating such as
polytetrafluoroethylene ("PTFE") or silicone containing coatings.
The invention is especially useful for forming longer life coatings
on aluminum substrates by pre-coating the substrate with an
anodized layer of titanium and/or zirconium oxide that provides
excellent corrosion-, heat- and abrasion-resistance in a hard yet
flexible film.
Inventors: |
Dolan; Shawn E. (Sterling
Heights, MI) |
Assignee: |
Henkel AG & Co. KGaA
(Duesseldorf, DE)
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Family
ID: |
36228373 |
Appl.
No.: |
11/156,425 |
Filed: |
June 20, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060013986 A1 |
Jan 19, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10972592 |
Oct 25, 2004 |
7569132 |
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10162965 |
Jun 5, 2002 |
6916414 |
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10033554 |
Oct 19, 2001 |
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09968023 |
Oct 2, 2001 |
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Current U.S.
Class: |
428/472.2;
428/472; 428/469 |
Current CPC
Class: |
C25D
11/18 (20130101); C23C 4/02 (20130101); C25D
11/30 (20130101); C23C 28/042 (20130101); C23C
28/00 (20130101); C25D 11/246 (20130101); C25D
11/06 (20130101); C25D 11/08 (20130101); C25D
11/026 (20130101); C25D 9/06 (20130101); C23C
22/361 (20130101); Y10T 428/18 (20150115); Y02T
50/60 (20130101) |
Current International
Class: |
B32B
15/04 (20060101) |
Field of
Search: |
;428/650,632,633,651,660,421,422,447,934 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1392284 |
|
Jan 2003 |
|
CN |
|
28 90 65 |
|
Apr 1991 |
|
DE |
|
289054 |
|
Apr 1991 |
|
DE |
|
41 04 847 |
|
Aug 1992 |
|
DE |
|
0259657 |
|
Mar 1988 |
|
EP |
|
0594374 |
|
Apr 1994 |
|
EP |
|
0823496 |
|
Feb 1998 |
|
EP |
|
0978576 |
|
Feb 2000 |
|
EP |
|
1002644 |
|
May 2000 |
|
EP |
|
0780494 |
|
Nov 2002 |
|
EP |
|
1407832 |
|
Feb 2004 |
|
EP |
|
25 49 092 |
|
May 1983 |
|
FR |
|
2657090 |
|
Nov 1995 |
|
FR |
|
294237 |
|
Sep 1929 |
|
GB |
|
493935 |
|
Oct 1938 |
|
GB |
|
1051665 |
|
Dec 1966 |
|
GB |
|
1319912 |
|
Jun 1973 |
|
GB |
|
2158842 |
|
Nov 1985 |
|
GB |
|
2343681 |
|
Jul 2000 |
|
GB |
|
5311133 |
|
Feb 1978 |
|
JP |
|
57 060098 |
|
Apr 1982 |
|
JP |
|
05287587 |
|
Aug 1982 |
|
JP |
|
57131391 |
|
Aug 1982 |
|
JP |
|
58 001093 |
|
Jan 1983 |
|
JP |
|
59 016994 |
|
Jan 1984 |
|
JP |
|
63100194 |
|
May 1986 |
|
JP |
|
63087716 |
|
Apr 1988 |
|
JP |
|
4308093 |
|
Oct 1992 |
|
JP |
|
2000248398 |
|
Sep 2000 |
|
JP |
|
3132133 |
|
Feb 2001 |
|
JP |
|
2049162 |
|
Nov 1995 |
|
RU |
|
2112087 |
|
May 1998 |
|
RU |
|
617493 |
|
Jul 1978 |
|
SU |
|
WO 92/14868 |
|
Sep 1992 |
|
WO |
|
WO 98/42892 |
|
Mar 1998 |
|
WO |
|
WO 98/42895 |
|
Oct 1998 |
|
WO |
|
WO 99/02759 |
|
Jan 1999 |
|
WO |
|
WO 00/03069 |
|
Jan 2000 |
|
WO |
|
WO 02/28838 |
|
Apr 2002 |
|
WO |
|
WO 03/029529 |
|
Apr 2003 |
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WO |
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WO 2006/047500 |
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May 2006 |
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WO |
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Other References
US. Appl. No. 10/972,591, filed Oct. 25, 2004, Dolan co-pending
application. cited by other .
U.S. Appl. No. 10/972,594, filed Oct. 25, 2004, Dolan co-pending
application. cited by other .
U.S. Appl. No. 10/972,592, filed Oct. 25, 2004, Dolan co-pending
application. cited by other .
Zozulin, Alex J.; "A Chromate-Free Anodize Process for Magnesium
Alloys: A Coating with Superior Characteristics", pp. 47-63. cited
by other .
Zozulin, et al.; "Anodized Coatings for magnesium Alloys", Metal
Finishing, Mar. 1994, pp. 39-44. cited by other .
IBM Technical Disclosure Bulletin, "Forming Protective Coatings on
Magnesium Alloys", Dec. 1967, p. 862. cited by other .
Barton, et al.; "The Effect of Electrolyte on the Anodized Finish
of a magnesium Alloy"; Plating & Surface Finishing, pp.
138-141, May 1995. cited by other .
Jacobson, et al.; "American Electroplaters and Surface Finishers
Society", pp. 541-549. cited by other .
Surface and Coatings Technology 122, "Plazma Electrolysis for
Surface Engineering", (1999), pp. 73-93. cited by other .
Galvanotechnik, "Plasmachemische Oxidationsverfahren Teil 1:
Historie und Verfahrensgrundlagen", (Apr. 2003), pp. 816-823. cited
by other .
Galvanotechnik, "Plasmachemische Oxidationsverfahren Teil 2:
Apparative Voraussetzungen", Jun. 2003, pp. 1374-1382. cited by
other .
Galvanotechnik, Plasmachemische Oxidationsverfahren Teil 3 Neue
Schicht-systeme, aussergewoehnliche Substratmaterialien und deren
gegenwaetige und zukueftige Anwendungsfelder, (Jul. 2003), pp.
1634-1645. cited by other .
Sworn Declaration of Dr. Peter Kurze dated Jul. 5, 2000, submitted
in connection with PCT Publication WO96/28591 of Magnesiu
Technology Limited. cited by other .
JP 05287587 Abstract. cited by other .
Zhou, Y. et al, "Electrochemical Deposition and Microstructure of
Copper (I) Oxide Films", Scripta Materials, vol. 38, No. 11 pp.
1731-1738 (1998). cited by other .
Yoshimura et al, "Recent developments in soft, solution processing.
one step fabrication of functional double oxide films by
hydrothermal-electrochemical methods", Journal of Materials
Chemistry, vol. 9, pp. 77-82 (1999). cited by other .
International Search Report dated Jan. 4, 2007, PCT International
Application PCT/US05/38337. cited by other .
Written Opinion dated Jan. 4, 2007, PCT International Application
PCT/US05/38337. cited by other .
Supplementary European Search Report, EP 05 81 2094, dated May 3,
2010. cited by other.
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Primary Examiner: Zimmerman; John J
Attorney, Agent or Firm: Cameron; Mary
Parent Case Text
This application is a continuation-in-part of application Ser. No.
10/972,592, filed Oct. 25, 2004, now U.S. Pat. No. 7,569,132 which
is a continuation-in-part of application Ser. No. 10/162,965, filed
Jun. 5, 2002, now U.S. Pat. No. 6,916,414 which is a
continuation-in-part of application Ser. No. 10/033,554, filed Oct.
19, 2001, now abandoned which is a continuation-in-part of
application Ser. No. 09/968,023, filed Oct. 2, 2001, now abandoned
each of which are incorporated herein by reference.
Claims
What is claimed is:
1. An article of manufacture made according to a method comprising:
A) providing an anodizing solution comprised of water and one or
more additional components selected from the group consisting of:
a) water-soluble complex fluorides, b) water-soluble complex
oxyfluorides, c) water-dispersible complex fluorides, and d)
water-dispersible complex oxyfluorides of elements selected from
the group consisting of Ti, Zr, Hf, Sn, Al, Ge and B and mixtures
thereof; B) providing a cathode in contact with said anodizing
solution; C) placing a metal article comprising aluminum or
aluminum alloy as an anode in said anodizing solution; D) passing a
current between the anode and cathode through said anodizing
solution for a time effective to form an adherent first protective
coating on the surface of the metal article; E) removing the metal
article having a first protective coating from the anodizing
solution and drying said article; and F) applying one or more
layers of coating material to the metal article having a first
protective coating, to form a second protective coating layer
either different from the first protective coating layer or having
the same composition as the first protective coating layer and
deposited non-anodically.
2. An article of manufacture comprising: a) a substrate having at
least one surface comprising at least 30 wt % aluminum; b) an acid
and alkali resistant, adherent first protective layer comprising
titanium dioxide and/or zirconium oxide deposited on said surface;
and c) a second protective layer adhered to said first protective
layer, the second protective layer either different from the first
protective coating layer or having the same composition as the
first protective coating layer and deposited non-anodically;
wherein said article exhibits less than 1% delamination in ASTM D
3359 testing and/or exhibits no corrosion after 1000 hours of ASTM
B-117-03 salt fog testing.
3. The article of claim 2, wherein the second protective layer
comprises an inner coating material layer substantially free of
PTFE and an outer paint layer comprising PTFE.
4. The article of claim 2 wherein the adherent first protective
layer is predominantly comprised of titanium dioxide.
5. The article of claim 2 wherein the second protective coating
layer comprises a thermal spray applied coating and/or one of PTFE
and silicone.
6. The article of claim 4 wherein the adherent first protective
layer predominantly comprised of titanium dioxide, further
comprises phosphorus.
7. The article of claim 2 wherein the second protective layer is
different from the first protective coating layer.
8. The article of claim 2 wherein the second protective layer has
the same chemical composition as the first protective coating layer
and is deposited non-anodically.
9. The article of claim 2 wherein the second protective layer
comprises both organic and inorganic substances.
10. The article of claim 2 wherein the second protective layer is
an organic coating.
11. The article of claim 2 wherein the second protective layer is
an inorganic coating.
12. The article of claim 2 wherein the second protective layer is a
paint.
13. The article of claim 2 wherein the second protective layer is a
thermal spray applied coating.
14. The article of claim 13 wherein the thermal spray applied
coating is selected from titania, alumina composite, zirconia
composite, and a coating comprising Fe, Mo and C.
15. The article of claim 14 wherein the thermal spray applied
coating is titania.
16. The article of claim 2 wherein the first protective layer
further comprises niobium, molybdenum, manganese, and/or
tungsten.
17. The article of claim 1 wherein the second protective layer is
different from the first protective coating layer.
18. The article of claim 1 wherein the second protective layer has
the same chemical composition as the first protective coating layer
and is deposited non-anodically.
19. The article of claim 1 wherein the second protective layer
comprises both organic and inorganic substances.
20. The article of claim 1 wherein the second protective layer is
an organic coating.
21. The article of claim 1 wherein the second protective layer is
an inorganic coating.
22. The article of claim 1 wherein the second protective layer is a
paint.
23. The article of claim 1 wherein the second protective layer is a
thermal spray applied coating.
24. The article of claim 23 wherein the thermal spray applied
coating is selected from titania, alumina composite, zirconia
composite, and a coating comprising Fe, Mo and C.
Description
FIELD OF THE INVENTION
This invention relates to anodically applied electrodeposited
coating of aluminum and aluminum alloy workpieces to provide
coatings comprising titanium and/or zirconium oxides, and the
subsequent coating of the anodized workpiece with organic coatings,
inorganic coatings and/or coatings that contain both organic and
inorganic substances. Particular examples of subsequent coatings
include paints, thermal spray applied coatings and coatings
comprising polytetrafluoroethylene (hereinafter referred to as
"PTFE") or silicone. The invention is especially useful for forming
longer life thermal spray applied, PTFE or silicone non-stick
coatings on aluminum substrates.
BACKGROUND OF THE INVENTION
Aluminum and its alloys have found a variety of industrial
applications. However, because of the reactivity of aluminum and
its alloys, and their tendency toward corrosion and environmental
degradation, it is necessary to provide the exposed surfaces of
these metals with an adequate corrosion-resistant and protective
coating. Further, such coatings should resist abrasion so that the
coatings remain intact during use, where the metal article may be
subjected to repeated contact with other surfaces, particulate
matter and the like. Where the appearance of articles fabricated is
considered important, the protective coating applied thereto should
additionally be uniform and decorative.
In order to provide an effective and permanent protective coating
on aluminum and its alloys, such metals have been anodized in a
variety of electrolyte solutions, such as sulfuric acid, oxalic
acid and chromic acid, which produce an alumina coating on the
substrate. While anodization of aluminum and its alloys is capable
of forming a more effective coating than painting or enameling, the
resulting coated metals have still not been entirely satisfactory
for their intended uses. The coatings frequently lack one or more
of the desired degree of flexibility, hardness, smoothness,
durability, adherence, heat resistance, resistance to acid and
alkali attack, corrosion resistance, and/or imperviousness required
to meet the most demanding needs of industry.
Heat resistance is a very desirable feature of a protective coating
for aluminum and its alloys. In the cookware industry, for
instance, aluminum is a material of choice due to its light weight
and rapid heat conduction properties. However, bare aluminum is
subject to corrosion and discoloration, particularly when exposed
to ordinary food acids such as lemon juice and vinegar, as well as
alkali, such as dishwasher soap. PTFE or silicone containing paints
are a common heat resistant coating for aluminum, which provide
resistance to corrosion and discoloration and provide a "non-stick"
cooking surface. However, PTFE containing paints have the drawback
of insufficient adherence to the substrate to resist peeling when
subjected to abrasion. To improve adherence of PTFE coatings,
manufacturers generally must provide three coats of paint on the
aluminum substrate: a primer, a midlayer and finally a topcoat
containing PTFE. This three-step process is costly and does not
solve the problem of insufficient abrasion resistance and the
problem of subsequent corrosion of the underlying aluminum when the
protective paint, in particular the PTFE coating wears off.
Likewise, the non-stick silicone coatings eventually wear away and
the underlying aluminum is exposed to acid, alkali and corrosive
attack.
To improve toughness and abrasion resistance, it is known in the
cookware industry to anodize aluminum to deposit a coating of
aluminum oxide, using a strongly acidic bath (pH<1), and to
thereafter apply a non-stick seal coating containing PTFE. A
drawback of this method is the nature of the anodized coating
produced. The aluminum oxide coating is not as impervious to acid
and alkali as oxides of titanium and/or zirconium. Articles coated
using this known process lose their PTFE coatings with repeated
exposure to typical dishwasher cycles of hot water and alkaline
cleaning agents.
So called, hard anodizing aluminum results in a harder coating of
aluminum oxide, deposited by anodic coating at pH<1 and
temperatures of less than 3.degree. C., which generates an alpha
phase alumina crystalline structure that still lacks sufficient
resistance to corrosion and alkali attack.
Thus, there is still considerable need to develop alternative
anodization processes for aluminum and its alloys which do not have
any of the aforementioned shortcomings and yet still furnish
adherent, corrosion-, heat- and abrasion-resistant protective
coatings of high quality and pleasing appearance.
In another known attempt to provide a corrosion-, heat- and
abrasion-resistant coating to support adherence of PTFE to
aluminum, an aluminum alloy was thermally sprayed with titanium
dioxide to generate a film that is physically adhered to the
underlying aluminum. This film had some adherence to the aluminum
article, but showed voids in the coating that are undesirable.
Thermal spraying technology involves heating and projecting
particles onto a prepared surface. Most metals, oxides, cermets,
hard metallic compounds, some organic plastics and certain glasses
may be deposited by one or more of the known thermal spray
processes. Feedstock may be in the form of powder, wire, flexible
powder-carrying tubes or rods depending on the particular process.
As the material passes through the spray gun, it is heated to a
softened or molten state, accelerated and, in the case of wire or
rod, atomized. A confined stream of hot particles generated in this
manner is propelled to the substrate and as the particles strike
the substrate surface they flatten and form thin platelets which
conform and adhere to the irregularities of the previously prepared
surface as well as to each other. Either the gun or the substrate
may be translated and the sprayed material builds up particle by
particle into a lamellar structure which forms a coating. This
particular coating technique has been in use for a number of years
as a means of surface restoration and protection. In aerospace,
aluminum components are often coated with thermal spray coatings of
zirconia and yttria to provide a thermal barrier. A newer variation
includes cold spray material deposition, which involves directing
particles of a coating material toward the target surface at a
velocity sufficiently high to cause the particles to deform and to
adhere to the target surface. Various aspects of thermal spray
coating are taught in U.S. Pat. Nos. 4,370,538; 4,869,936;
5,302,414; 6,082,444; 6,861,101; 6,863,990; 6,869,703; 6,875,529;
incorporated herein by reference.
It has now been discovered that surprising improvements in
performance of thermal spray coated products can be achieved by
depositing an underlayer according to the invention on an aluminum
alloy substrate and then depositing the thermal spray coating on
the oxide underlayer of the invention.
SUMMARY OF THE INVENTION
Applicant has developed a process whereby articles of aluminum or
aluminum alloy may be rapidly coated with anodically applied
electrodeposited coating to form protective coatings that are
resistant to corrosion and abrasion using anodizing solutions
containing complex fluorides and/or complex oxyfluorides. The
anodizing solution is aqueous and comprises one or more components
selected from water-soluble and water-dispersible complex fluorides
and oxyfluorides of elements selected from the group consisting of
Ti, Zr, Hf, Sn, Al, Ge and B. The use of the term "solution" herein
is not meant to imply that every component present is necessarily
fully dissolved and/or dispersed. Some anodizing solutions of the
invention comprise a precipitate or develop a small amount of
sludge in the bath during use, which does not adversely affect
performance. In especially preferred embodiments of the invention,
the anodizing solution comprises one or more components selected
from the group consisting of the following: a) water-soluble and/or
water-dispersible phosphorus oxysalts, wherein the phosphorus
concentration in the anodizing solution is at least 0.01M; b)
water-soluble and/or water-dispersible complex fluorides of
elements selected from the group consisting of Ti, Zr, Hf, Sn, Al,
Ge and B; c) water-soluble and/or water-dispersible zirconium
oxysalts; d) water-soluble and/or water-dispersible vanadium
oxysalts; e) water-soluble and/or water-dispersible titanium
oxysalts; f) water-soluble and/or water-dispersible alkali metal
fluorides; g) water-soluble and/or water-dispersible niobium salts;
h) water-soluble and/or water-dispersible molybdenum salts; i)
water-soluble and/or water-dispersible manganese salts; j)
water-soluble and/or water-dispersible tungsten salts; and k)
water-soluble and/or water-dispersible alkali metal hydroxides.
In one embodiment of the invention, niobium, molybdenum, manganese,
and/or tungsten salts are co-deposited in a ceramic oxide film of
zirconium and/or titanium.
The method of the invention comprises providing a cathode in
contact with the anodizing solution, placing the article as an
anode in the anodizing solution, and passing a current through the
anodizing solution at a voltage and for a time effective to form
the anodically applied electrodeposited protective coating on the
surface of the article. Pulsed direct current or alternating
current is generally preferred. Non-pulsed direct current may also
be used. When using pulsed current, the average voltage is
preferably not more than 250 volts, more preferably, not more than
200 volts, or, most preferably, not more than 175 volts, depending
on the composition of the anodizing solution selected. The peak
voltage, when pulsed current is being used, is preferably not more
than 600, most preferably 500 volts. In one embodiment, the peak
voltage for pulsed current is not more than, in increasing order of
preference 600, 575, 550, 525, 500, 480, 450 volts and
independently not less than 300, 310, 320, 330, 340, 350, 360, 370,
380, 390, 400 volts. When alternating current is being used, the
voltage may range from about 200 to about 600 volts. In another
alternating current embodiment, the voltage is, in increasing order
of preference 600, 575, 550, 525, 500 volts and independently not
less than 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400
volts. In the presence of phosphorus containing components,
non-pulsed direct current, also known as straight direct current,
may be used at voltages from about 200 to about 600 volts. The
non-pulsed direct current desirably has a voltage of, in increasing
order of preference 600, 575, 550, 525, 500 volts and independently
not less than 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400
volts.
It is an object of the invention to provide a method of forming a
protective coating on a surface of a metal article comprising
aluminum or aluminum alloy, the method comprising: providing an
anodizing solution comprised of water and one or more additional
components selected from the group consisting of water-soluble
complex fluorides, water-soluble complex oxyfluorides,
water-dispersible complex fluorides, and water-dispersible complex
oxyfluorides of elements selected from the group consisting of Ti,
Zr, Hf, Sn, Al, Ge and B and mixtures thereof; providing a cathode
in contact with the anodizing solution; placing a metal article
comprising aluminum or aluminum alloy as an anode in the
electrodeposition anodizing solution; passing a current between the
anode and cathode through the solution for a time effective to form
a first protective coating on the surface of the metal article;
removing the metal article having a first protective coating from
the anodizing solution and drying the article; and applying one or
more layers of coating material to the metal article having a first
protective coating, preferably at least one of the layers
comprising a thermal spray applied material such as metal, oxide,
organic substances and mixtures thereof, PTFE or silicone, to form
a second protective coating.
It is a further object of the invention to provide a method wherein
the first protective coating comprises titanium dioxide and/or
zirconium oxide. It is a yet further object of the invention to
provide a method wherein the first protective coating is comprised
of titanium dioxide and the current is direct current.
It is a further object of the invention to provide a method wherein
the anodizing solution is maintained at a temperature of from
0.degree. C. to 90.degree. C. It is also a further object of the
invention to provide a method wherein the current is pulsed direct
current having an average voltage of not more than 200 volts. It is
a further object of the invention to provide a method wherein the
metal article is aluminum and the current is direct current or
alternating current. It is a further object of the invention to
provide a method wherein the current is pulsed direct current.
It is a further object of the invention to provide a method wherein
the protective coating is formed at a rate of at least 1 micron
thickness per minute.
It is a further object of the invention to provide a method wherein
the second protective coating comprises a non-stick topcoat
comprising PTFE or silicone and at least one additional coating
layer, such as paint or thermal spray applied material, between the
topcoat and the first protective coating.
It is a further object of the invention to provide a method wherein
the anodizing solution is prepared using a complex fluoride
selected from the group consisting of H2TiF6, H2ZrF6, H2HfF6,
H2SnF6, H2GeF6, H3AlF6, HBF4 and salts and mixtures thereof and
optionally comprises HF or a salt thereof.
It is a further object of the invention to provide a method wherein
the anodizing solution is additionally comprised of a phosphorus
containing acid and/or salt, and/or a chelating agent. Preferably,
the phosphorus containing acid and/or salt comprises one or more of
a phosphoric acid, a phosphoric acid salt, a phosphorous acid and a
phosphorous acid salt. It is a further object of the invention to
provide a method wherein pH of the anodizing solution is adjusted
using ammonia, an amine, an alkali metal hydroxide or a mixture
thereof.
It is an object of the invention to provide a method of forming a
protective coating on a surface of a metallic article comprised
predominantly of aluminum, the method comprising: providing an
anodizing solution comprised of water, a phosphorus containing acid
and/or salt, and one or more additional components selected from
the group consisting of water-soluble and water-dispersible complex
fluorides and mixtures thereof, the fluorides comprising elements
selected from the group consisting of Ti, Zr, and combinations
thereof; providing a cathode in contact with the anodizing
solution; placing a metallic article comprised predominantly of
aluminum as an anode in the anodizing solution; passing a direct
current or an alternating current between the anode and the cathode
for a time effective to form a first protective coating on the
surface of the metal article; removing the metal article having a
first protective coating from the anodizing solution and drying the
article; and applying one or more layers of coating material to the
metal article having a first protective coating, at least one of
the layers comprising a thermal spray applied coating, PTFE or
silicone, to form a second protective coating.
It is a further object of the invention to provide a method wherein
the anodizing solution is prepared using a complex fluoride
comprising an anion comprising at least 4 fluorine atoms and at
least one atom selected from the group consisting of Ti, Zr, and
combinations thereof.
It is a further object of the invention to provide a method wherein
the anodizing solution is prepared using a complex fluoride
selected from the group consisting of H2TiF6, H2ZrF6, salts of
H2TiF6, salts of H2ZrF6, and mixtures thereof.
It is a further object of the invention to provide a method wherein
the complex fluoride is introduced into the anodizing solution at a
concentration of at least 0.05M.
It is a further object of the invention to provide a method wherein
the direct current has an average voltage of not more than 250
volts.
It is a further object of the invention to provide a method wherein
the anodizing solution is additionally comprised of a chelating
agent.
It is a further object of the invention to provide a method wherein
the anodizing solution is comprised of at least one complex
oxyfluoride prepared by combining at least one complex fluoride of
at least one element selected from the group consisting of Ti, Zr,
and at least one compound which is an oxide, hydroxide, carbonate
or alkoxide of at least one element selected from the group
consisting of Ti, Zr, Hf, Sn, B, Al and Ge.
It is a further object of the invention to provide a method wherein
the anodizing solution has a pH of from about 2 to about 6.
It is an object of the invention to provide a method of forming a
protective coating on an article having a metallic surface
comprised of aluminum or aluminum alloy, the method comprising:
providing an anodizing solution, the anodizing solution having been
prepared by dissolving a water-soluble complex fluoride and/or
oxyfluoride of an element selected from the group consisting of Ti,
Zr, Hf, Sn, Ge, B and combinations thereof and an inorganic acid or
salt thereof that contains phosphorus in water; providing a cathode
in contact with the anodizing solution; placing an article
comprising at least one metallic surface comprised of aluminum or
aluminum alloy as an anode in the anodizing solution; passing a
direct current or an alternating current between the anode and the
cathode for a time effective to form a first protective coating on
the at least one metallic surface; removing the article comprising
at least one metallic surface having a first protective coating
from the anodizing solution and drying the article; and applying
one or more layers of coating material to the first protective
coating, at least one of the layers comprising a thermal spray
applied coating, PTFE or silicone, to form a second protective
coating.
It is a further object of the invention to provide a method wherein
pH of the anodizing solution is adjusted using ammonia, an amine,
an alkali metal hydroxide or a mixture thereof.
It is a further object of the invention to provide a method wherein
the current is pulsed direct current having an average voltage of
not more than 150 volts (Higher average voltages may be used,
however, they are generally less economical in power consumed).
It is a further object of the invention to provide a method wherein
at least one compound which is an oxide, hydroxide, carbonate or
alkoxide of at least one element selected from the group consisting
of Ti, Zr, Hf, Sn, B, Al and Ge is additionally used to prepare the
anodizing solution.
It is an object of the invention to provide a method of forming a
protective coating on a surface of an article comprised of
aluminum, the method comprising: providing an anodizing solution,
the anodizing solution having been prepared by combining one or
more water-soluble complex fluorides of titanium and/or zirconium
or salts thereof, a phosphorus containing oxy acid and/or salt and
optionally, an oxide, hydroxide, carbonate or alkoxide of
zirconium; providing a cathode in contact with the anodizing
solution; placing an article comprised of aluminum as an anode in
the anodizing solution; and passing a direct current or an
alternating current between the anode and the cathode for a time
effective to form the protective coating on a surface of the
article; removing the article having a first protective coating
from the anodizing solution and drying the article; and applying
one or more layers of coating material to the article having a
first protective coating, at least one of the layers comprising a
thermal spray applied coating, PTFE or silicone, to form a second
protective coating.
It is a further object of the invention to provide a method wherein
one or more of H2TiF6, salts of H2TiF6, H2ZrF6, and salts of H2ZrF6
is used to prepare the anodizing solution. It is a further object
of the invention to provide a method wherein zirconium basic
carbonate is also used to prepare the anodizing solution. It is a
further object of the invention to provide a method wherein the one
or more water-soluble complex fluorides is a complex fluoride of
titanium or zirconium and the current is direct current, pulsed or
non-pulsed.
DETAILED DESCRIPTION OF THE INVENTION
Except in the claims and the operating examples, or where otherwise
expressly indicated, all numerical quantities in this description
indicating amounts of material or conditions of reaction and/or use
are to be understood as modified by the word "about" in describing
the scope of the invention. Practice within the numerical limits
stated is generally preferred, however. Also, throughout the
description, unless expressly stated to the contrary: percent,
"parts of", and ratio values are by weight or mass; the description
of a group or class of materials as suitable or preferred for a
given purpose in connection with the invention implies that
mixtures of any two or more of the members of the group or class
are equally suitable or preferred; description of constituents in
chemical terms refers to the constituents at the time of addition
to any combination specified in the description or of generation in
situ within the composition by chemical reaction(s) between one or
more newly added constituents and one or more constituents already
present in the composition when the other constituents are added;
specification of constituents in ionic form additionally implies
the presence of sufficient counterions to produce electrical
neutrality for the composition as a whole and for any substance
added to the composition; any counterions thus implicitly specified
preferably are selected from among other constituents explicitly
specified in ionic form, to the extent possible; otherwise, such
counterions may be freely selected, except for avoiding counterions
that act adversely to an object of the invention; the term "thermal
spray", "thermal spray applied coating" and grammatical variations
include the process and coating made by the process of directing
heated or unheated particles of a coating material toward a target
surface at a velocity sufficiently high to cause the particles to
adhere to the target surface and includes, by way of non-limiting
example, cold spray, plasma spray, low pressure plasma spray
(LPPS), air plasma spray (APS) and high velocity oxy-fuel (HVOF),
powder flame spray, wire/rod flame spray, detonation/explosive
flame spray and wire arc spray and similar processes known in the
industry; the term "paint" and its grammatical variations includes
any more specialized types of protective exterior coatings that are
also known as, for example, lacquer, electropaint, shellac,
porcelain enamel, top coat, mid coat, base coat, color coat, and
the like; the word "mole" means "gram mole", and the word itself
and all of its grammatical variations may be used for any chemical
species defined by all of the types and numbers of atoms present in
it, irrespective of whether the species is ionic, neutral,
unstable, hypothetical or in fact a stable neutral substance with
well defined molecules; and the terms "solution", "soluble",
"homogeneous", and the like are to be understood as including not
only true equilibrium solutions or homogeneity but also
dispersions.
There is no specific limitation on the aluminum or aluminum alloy
article to be subjected to anodization in accordance with the
present invention. It is desirable that at least a portion of the
article is fabricated from a metal that contains not less than 50%
by weight, more preferably not less than 70% by weight aluminum.
Preferably, the article is fabricated from a metal that contains
not less than, in increasing order of preference, 30, 40, 50, 60,
70, 80, 90, 100% by weight aluminum.
In carrying out the anodically applied electrodeposited coating of
a workpiece, an anodizing solution is employed which is preferably
maintained at a temperature between about 0.degree. C. and about
90.degree. C. It is desirable that the temperature be at least
about, in increasing order of preference 5, 10, 15, 20, 25, 30, 40,
50.degree. C. and not more than 90, 88, 86, 84, 82, 80, 75, 70,
65.degree. C.
The anodically applied electrodeposited coating process comprises
immersing at least a portion of the workpiece in the anodizing
solution, which is preferably contained within a bath, tank or
other such container. The article (workpiece) functions as the
anode. A second metal article that is cathodic relative to the
workpiece is also placed in the anodizing solution. Alternatively,
the anodizing solution is placed in a container which is itself
cathodic relative to the workpiece (anode). When using pulsed
current, an average voltage potential not in excess of in
increasing order of preference 250 volts, 200 volts, 175 volts, 150
volts, 125 volts, 120 volts, 115 volts is then applied across the
electrodes until a coating of the desired thickness is formed on
the surface of the aluminum article in contact with the anodizing
solution. When certain anodizing solution compositions are used,
good results may be obtained even at average voltages not in excess
of 100 volts. It has been observed that the formation of a
corrosion- and abrasion-resistant protective coating is often
associated with anodization conditions which are effective to cause
a visible light-emitting discharge (sometimes referred to herein as
a "plasma", although the use of this term is not meant to imply
that a true plasma exists) to be generated (either on a continuous
or intermittent or periodic basis) on the surface of the aluminum
article.
In one embodiment, direct current (DC) is used at 10-400
Amps/square foot and 200 to 600 volts. In another embodiment, the
current is pulsed or pulsing current. Non-pulsed direct current is
desirably used in the range of 200-600 volts; preferably the
voltage is at least, in increasing order of preference 200, 250,
300, 350, 400 and at least for the sake of economy, not more than
in increasing order of preference 700, 650, 600, 550. Direct
current is preferably used, although alternating current may also
be utilized (under some conditions, however, the rate of coating
formation may be lower using AC). The frequency of the current may
range from 10 to 10,000 Hertz; higher frequencies may be used. In
embodiments where AC power is used, 300 to 600 volts is the
preferred voltage level.
In a preferred embodiment, the pulsed signal may have an "off" time
between each consecutive voltage pulse preferably lasting between
about 10% as long as the voltage pulse and about 1000% as long as
the voltage pulse. During the "off" period, the voltage need not be
dropped to zero (i.e., the voltage may be cycled between a
relatively low baseline voltage and a relatively high ceiling
voltage). The baseline voltage thus may be adjusted to a voltage
that is from 0% to 99.9% of the peak applied ceiling voltage. Low
baseline voltages (e.g., less than 30% of the peak ceiling voltage)
tend to favor the generation of a periodic or intermittent visible
light-emitting discharge, while higher baseline voltages (e.g.,
more than 60% of the peak ceiling voltage) tend to result in
continuous plasma anodization (relative to the human eye frame
refresh rate of 0.1-0.2 seconds). The current can be pulsed with
either electronic or mechanical switches activated by a frequency
generator. The average amperage per square foot is at least in
increasing order of preference 10, 20, 30, 40, 50, 60, 70, 80, 90,
100, 105, 110, 115, and not more than at least for economic
considerations in increasing order of preference 300, 275, 250,
225, 200, 180, 170, 160, 150, 140, 130, 125. More complex waveforms
may also be employed, such as, for example, a DC signal having an
AC component. Alternating current may also be used, with voltages
desirably between about 200 and about 600 volts. The higher the
concentration of the electrolyte in the anodizing solution, the
lower the voltage can be while still depositing satisfactory
coatings.
A number of different types of anodizing solutions may be
successfully used in the process of this invention, as will be
described in more detail hereinafter. However, it is believed that
a wide variety of water-soluble or water-dispersible anionic
species containing metal, metalloid, and/or non-metal elements are
suitable for use as components of the anodizing solution. Suitable
elements include, for example, phosphorus, titanium, zirconium,
hafnium, tin, germanium, boron, vanadium, fluoride, zinc, niobium,
molybdenum, manganese, tungsten and the like (including
combinations of such elements). In a preferred embodiment of the
invention, the components of the anodizing solution are titanium
and/or zirconium.
Without wishing to be bound by theory, it is thought that the
anodically applied electrodeposited coating of aluminum and
aluminum alloy articles in the presence of complex fluoride or
oxyfluoride species to be described subsequently in more detail
leads to the formation of surface films comprised of
metal/metalloid oxide ceramics (including partially hydrolyzed
glasses containing O, OH and/or F ligands) or metal/non-metal
compounds wherein the metal comprising the surface film includes
metals from the complex fluoride or oxyfluoride species and some
metals from the article. From analysis of coatings of the Examples,
it appears that the majority of metals in the coating come from the
anodizing solution. The glow, plasma or sparking which often occurs
during anodically applied electrodeposited coating in accordance
with the present invention is believed to destabilize the anionic
species, causing certain ligands or substituents on such species to
be hydrolyzed or displaced by O and/or OH or metal-organic bonds to
be replaced by metal-O or metal-OH bonds. Such hydrolysis and
displacement reactions render the species less water-soluble or
water-dispersible, thereby driving the formation of the surface
coating.
A pH adjuster may be present in the anodizing solution; suitable pH
adjusters include, by way of nonlimiting example, ammonia, amine or
other base. The amount of pH adjuster is limited to the amount
required to achieve a pH of 2-11, preferably 2-8 and most
preferably 3-6; and is dependent upon the type of electrolyte used
in the anodizing bath. In a preferred embodiment, the amount of pH
adjuster is less than 1% w/v.
In certain embodiments of the invention, the anodizing solution is
essentially (more preferably, entirely) free of chromium,
permanganate, borate, sulfate, free fluoride and/or free
chloride.
The anodizing solution used preferably comprises water and at least
one complex fluoride or oxyfluoride of an element selected from the
group consisting of Ti, Zr, Hf, Sn, Al, Ge and B (preferably, Ti
and/or Zr). The complex fluoride or oxyfluoride should be
water-soluble or water-dispersible and preferably comprises an
anion comprising at least 1 fluorine atom and at least one atom of
an element selected from the group consisting of Ti, Zr, Hf, Sn,
Al, Ge or B. The complex fluorides and oxyfluorides (sometimes
referred to by workers in the field as "fluorometallates")
preferably are substances with molecules having the following
general empirical formula (I): H.sub.pT.sub.qF.sub.rO.sub.s (I)
wherein: each of p, q, r, and s represents a non-negative integer;
T represents a chemical atomic symbol selected from the group
consisting of Ti, Zr, Hf, Sn, Al, Ge, and B; r is at least 1; q is
at least 1; and, unless T represents B, (r+s) is at least 6. One or
more of the H atoms may be replaced by suitable cations such as
ammonium, metal, alkaline earth metal or alkali metal cations
(e.g., the complex fluoride may be in the form of a salt, provided
such salt is water-soluble or water-dispersible).
Illustrative examples of suitable complex fluorides include, but
are not limited to, H2TiF6, H2ZrF6, H2HfF6, H2GeF6, H2SnF6, H3AlF6,
and HBF4 and salts (fully as well as partially neutralized) and
mixtures thereof. Examples of suitable complex fluoride salts
include SrZrF6, MgZrF6, Na2ZrF6, Li2ZrF6, SrTiF6, MgTiF6, Na2TiF6
and Li2TiF6.
The total concentration of complex fluoride and complex oxyfluoride
in the anodizing solution preferably is at least about 0.005 M.
Generally, there is no preferred upper concentration limit, except
of course for any solubility constraints. It is desirable that the
total concentration of complex fluoride and complex oxyfluoride in
the anodizing solution be at least 0.005, 0.010, 0.020, 0.030,
0.040, 0.050, 0.060, 0.070, 0.080, 0.090, 0.10, 0.20, 0.30, 0.40,
0.50, 0.60 M, and if only for the sake of economy be not more than,
in increasing order of preference 2.0, 1.5, 1.0, 0.80 M.
To improve the solubility of the complex fluoride or oxyfluoride,
especially at higher pH, it may be desirable to include an
inorganic acid (or salt thereof) that contains fluorine but does
not contain any of the elements Ti, Zr, Hf, Sn, Al, Ge or B in the
electrolyte composition. Hydrofluoric acid or a salt of
hydrofluoric acid such as ammonium bifluoride is preferably used as
the inorganic acid. The inorganic acid is believed to prevent or
hinder premature polymerization or condensation of the complex
fluoride or oxyfluoride, which otherwise (particularly in the case
of complex fluorides having an atomic ratio of fluorine to "T" of
6) may be susceptible to slow spontaneous decomposition to form a
water-insoluble oxide. Certain commercial sources of
hexafluorotitanic acid and hexafluorozirconic acid are supplied
with an inorganic acid or salt thereof, but it may be desirable in
certain embodiments of the invention to add still more inorganic
acid or inorganic salt.
A chelating agent, especially a chelating agent containing two or
more carboxylic acid groups per molecule such as nitrilotriacetic
acid, ethylene diamine tetraacetic acid,
N-hydroxyethyl-ethylenediamine triacetic acid, or
diethylene-triamine pentaacetic acid or salts thereof, may also be
included in the anodizing solution. Other Group IV compounds may be
used, such as, by way of non-limiting example, Ti and/or Zr
oxalates and/or acetates, as well as other stabilizing ligands,
such as acetylacetonate, known in the art that do not interfere
with the anodic deposition of the anodizing solution and normal
bath lifespan. In particular, it is necessary to avoid organic
materials that either decompose or undesirably polymerize in the
energized anodizing solution.
Suitable complex oxyfluorides may be prepared by combining at least
one complex fluoride with at least one compound which is an oxide,
hydroxide, carbonate, carboxylate or alkoxide of at least one
element selected from the group consisting of Ti, Zr, Hf, Sn, B,
Al, or Ge. Examples of suitable compounds of this type that may be
used to prepare the anodizing solutions of the present invention
include, without limitation, zirconium basic carbonate, zirconium
acetate and zirconium hydroxide. The preparation of complex
oxyfluorides suitable for use in the present invention is described
in U.S. Pat. No. 5,281,282, incorporated herein by reference in its
entirety. The concentration of this compound used to make up the
anodizing solution is preferably at least, in increasing preference
in the order given, 0.0001, 0.001 or 0.005 moles/kg (calculated
based on the moles of the element(s) Ti, Zr, Hf, Sn, B, Al and/or
Ge present in the compound used). Independently, the ratio of the
concentration of moles/kg of complex fluoride to the concentration
in moles/kg of the oxide, hydroxide, carbonate or alkoxide compound
preferably is at least, with increasing preference in the order
given, 0.05:1, 0.1:1, or 1:1. In general, it will be preferred to
maintain the pH of the anodizing solution in this embodiment of the
invention in the range of from about 2 to about 11, more preferably
2-8, and in one embodiment a pH of 2-6.5 is desirable. A base such
as ammonia, amine or alkali metal hydroxide may be used, for
example, to adjust the pH of the anodizing solution to the desired
value.
Rapid coating formation is generally observed at average voltages
of 150 volts or less (preferably 100 or less), using pulsed DC. It
is desirable that the average voltage be of sufficient magnitude to
generate coatings of the invention at a rate of at least about 1
micron thickness per minute, preferably at least 3-8 microns in 3
minutes. If only for the sake of economy, it is desirable that the
average voltage be less than, in increasing order of preference,
150, 140, 130, 125, 120, 115, 110, 100, 90 volts. The time required
to deposit a coating of a selected thickness is inversely
proportional to the concentration of the anodizing bath and the
amount of current Amps/square foot used. By way of non-limiting
example, parts may be coated with an 8 micron thick metal oxide
layer in as little as 10-15 seconds at concentrations cited in the
Examples by increasing the Amps/square foot to 300-2000 amps/square
foot. The determination of correct concentrations and current
amounts for optimum part coating in a given period of time can be
made by one of skill in the art based on the teachings herein with
minimal experimentation.
Coatings of the invention are typically fine-grained and desirably
are at least 1 micron thick, preferred embodiments have coating
thicknesses from 1-20 microns, preferably 2-10 microns, most
preferably 3-9 microns. Thinner or thicker coatings may be applied,
although thinner coatings may not provide the desired coverage of
the article. Without being bound by a single theory, it is believed
that, particularly for insulating oxide films, as the coating
thickness increases the film deposition rate is eventually reduced
to a rate that approaches zero asymptotically. Add-on mass of
coatings of the invention ranges from approximately 5-200 g/m.sup.2
or more and is a function of the coating thickness and the
composition of the coating. It is desirable that the add-on mass of
coatings be at least, in increasing order of preference, 5, 10, 11,
12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50 g/m.sup.2.
An anodizing solution for use in forming a white protective coating
on an aluminum or aluminum alloy substrate may be prepared using
the following components:
TABLE-US-00001 Zirconium Basic Carbonate 0.01 to 1 wt. %
H.sub.2ZrF.sub.6 0.1 to 10 wt. % Water Balance to 100%
pH adjusted to the range of 2 to 5 using ammonia, amine or other
base.
In a preferred embodiment utilizing zirconium basic carbonate and
H.sub.2ZrF.sub.6, it is desirable that the anodizing solution
comprise zirconium basic carbonate in an amount of at least, in
increasing order of preference 0.05, 0.10, 0.15, 0.20, 0.25, 0.30,
0.35, 0.40, 0.45, 0.50, 0.55, 0.60 wt. % and not more than, in
increasing order of preference 1.0, 0.97, 0.95, 0.92, 0.90, 0.87,
0.85, 0.82, 0.80, 0.77 wt. %. In this embodiment, it is desirable
that the anodizing solution comprises H.sub.2ZrF.sub.6 in an amount
of at least, in increasing order of preference 0.2, 0.4, 0.6,
0.8.1.0, 1.2, 1.3, 1.4, 1.5, 2.0, 2.5, 3.0, 3.5, wt. % and not more
than, in increasing order of preference 10, 9.75, 9.5, 9.25, 9.0,
8.75, 8.5, 8.25, 8.0, 7.75 4.0, 4.5, 5.0, 5.5, 6.0 wt. %.
In a particularly preferred embodiment the amount of zirconium
basic carbonate ranges from about 0.75 to 0.25 wt. %, the
H.sub.2ZrF.sub.6 ranges from 6.0 to 9.5 wt %; a base such as
ammonia is used to adjust the pH to ranges from 3 to 5.
It is believed that the zirconium basic carbonate and the
hexafluorozirconic acid combine to at least some extent to form one
or more complex oxyfluoride species. The resulting anodizing
solution permits rapid anodization of aluminum-containing articles
using pulsed direct current having an average voltage of not more
than 175 volts. In this particular embodiment of the invention,
better coatings are generally obtained when the anodizing solution
is maintained at a relatively high temperature during anodization
(e.g., 40 degrees C. to 80 degrees C.). Alternatively, alternating
current preferably having a voltage of from 300 to 600 volts may be
used. The solution has the further advantage of forming protective
coatings that are white in color, thereby eliminating the need to
paint the anodized surface if a white decorative finish is desired.
The anodically applied electrodeposited coatings produced in
accordance with this embodiment of the invention typically have L
values of at least 80, high hiding power at coating thicknesses of
4 to 8 microns, and excellent acid, alkali and corrosion
resistance. To the best of the inventor's knowledge, no anodization
technologies being commercially practiced today are capable of
producing coatings having this desirable combination of
properties.
In another particularly preferred embodiment of the invention, the
anodizing solution used comprises water, a water-soluble or
water-dispersible phosphorus containing acid or salt, such as a
phosphorus oxyacid or salt, preferably an acid or salt containing
phosphate anion; and at least one of H2TiF6 and H2ZrF6. It is
desirable that the pH of the anodizing solution is neutral to acid,
6.5 to 1, more preferably, 6 to 2, most preferably 5-3.
It was surprisingly found that the combination of a phosphorus
containing acid and/or salt and the complex fluoride in the
anodizing solution produced a different type of anodically applied
electrodeposited coating. The oxide coatings deposited comprised
predominantly oxides of anions present in the anodizing solution
prior to any dissolution of the anode. That is, this process
results in coatings that result predominantly from deposition of
substances that are not drawn from the body of the anode, resulting
in less change to the substrate of the article being anodized.
In this embodiment, it is desirable that the anodizing solution
comprise the at least one complex fluoride, e.g. H2TiF6 and/or
H2ZrF6 in an amount of at least, in increasing order of preference
0.2, 0.4, 0.6, 0.8. 1.0, 1.2, 1.3, 1.4, 1.5, 2.0, 2.5, 3.0, 3.5 wt.
% and not more than, in increasing order of preference 10, 9.5,
9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5. 4.0 wt. %. The at
least one complex fluoride may be supplied from any suitable source
such as, for example, various aqueous solutions known in the art.
For H2TiF6 commercially available solutions typically range in
concentration from 50-60 wt %; while for H2ZrF6 such solutions
range in concentration between 20-50%.
The phosphorus oxysalt may be supplied from any suitable source
such as, for example, ortho-phosphoric acid, pyro-phosphoric acid,
tri-phosphoric acid, meta-phosphoric acid, polyphosphoric acid and
other combined forms of phosphoric acid, as well as phosphorous
acids, and hypo-phosphorous acids, and may be present in the
anodizing solution in partially or fully neutralized form (e.g., as
a salt, wherein the counter ion(s) are alkali metal cations,
ammonium or other such species that render the phosphorus oxysalt
water-soluble). Organophosphates such as phosphonates and the like
may also be used (for example, the various phosphonates available
from Rhodia Inc. and Solutia Inc.) provided that the organic
component does not interfere with the anodic deposition.
Particularly preferred is the use of a phosphorus oxysalt in acid
form. The phosphorus concentration in the anodizing solution is at
least 0.01 M. It is preferred that the concentration of phosphorus
in the anodizing solution be at least, in increasing order of
preference, 0.01M, 0.015, 0.02, 0.03, 0.04, 0.05, 0.07, 0.09, 0.10,
0.12, 0.14, 0.16. In embodiments where the pH of the anodizing
solution is acidic (pH<7), the phosphorus concentration can be
0.2 M, 0.3 M or more and preferably, at least for economy is not
more than 1.0, 0.9, 0.8, 0.7, 0.6 M. In embodiments where the pH is
neutral to basic, the concentration of phosphorus in the anodizing
solution is not more than, in increasing order of preference 0.40,
0.30, 0.25, 0.20 M.
A preferred anodizing solution for use in forming a protective
ceramic coating according to this embodiment on an aluminum or
aluminum alloy substrate may be prepared using the following
components:
TABLE-US-00002 H.sub.2TiF.sub.6 0.05 to 10 wt. % H.sub.3PO.sub.4
0.1 to 0.6 wt. % Water Balance to 100%
The pH is adjusted to the range of 2 to 6 using ammonia, amine or
other base.
With the aforedescribed anodizing solutions, the generation of a
sustained "plasma" (visible light emitting discharge) during
anodization is generally attained using pulsed DC having an average
voltage of no more than 150 volts. In preferred operation, the
average voltage does not exceed 100 volts.
The coatings produced in accordance with the invention typically
range in color from blue-grey and light grey to charcoal grey
depending upon the coating thickness and relative amounts of Ti and
Zr oxides in the coatings. The coatings exhibit high hiding power
at coating thicknesses of 2-10 microns, and excellent acid, alkali
and corrosion resistance. A test panel of a 400 series aluminum
alloy having anodically applied electrodeposited coating according
to a process of the invention had an 8-micron thick layer of
adherent ceramic predominantly comprising titanium dioxide. This
coated test panel was scratched down to bare metal prior to salt
fog testing. Despite being subjected to 1000 hours of salt fog
testing according to ASTM B-117-03, there was no corrosion
extending from the scribed line.
A commercially available bare aluminum wheel was cut into pieces
and the test specimen was anodically coated according to a process
of the invention with a 10-micron thick layer of ceramic
predominantly comprising titanium dioxide. Without being bound to a
single theory, the darker grey coating is attributed to the greater
thickness of the coating. The coating completely covered the
surfaces of the aluminum wheel including the design edges. The
coated aluminum wheel portion had a line scratched into the coating
down to bare metal prior to salt fog testing. Despite being
subjected to 1000 hours of salt fog according to ASTM B-117-03,
there is no corrosion extending from the scribed line and no
corrosion at the design edges. References to "design edges" will be
understood to include the cut edges as well as shoulders or
indentations in the article which have or create external corners
at the intersection of lines generated by the intersection of two
planes. The excellent protection of the design edges is an
improvement over conversion coatings, including chrome containing
conversion coatings, which show corrosion at the design edges after
similar testing.
In another aspect of the invention, Applicant surprisingly
discovered that titanium containing substrates and aluminum
containing substrates can be coated simultaneously in the anodizing
process of the invention. A titanium clamp was used to hold an
aluminum test panel during anodically applied electrodeposited
coating according to the invention and both substrates, the clamp
and the panel, were coated simultaneously according to the process
of the invention. Although the substrates do not have the same
composition, the coating on the surface appeared uniform and
monochromatic. The substrates were coated with an anodically
applied electrodeposited coating according to a process of the
invention with a 7-micron thick layer of ceramic predominantly
comprising titanium dioxide. The coating was a light grey in color,
and provided good hiding power.
Before being subjected to anodic treatment in accordance with the
invention, the aluminiferous metal article preferably is subjected
to a cleaning and/or degreasing step. For example, the article may
be chemically degreased by exposure to an alkaline cleaner such as,
for example, a diluted solution of PARCO Cleaner 305 (a product of
the Henkel Surface Technologies division of Henkel Corporation,
Madison Heights, Mich.). After cleaning, the article preferably is
rinsed with water. Cleaning may then, if desired, be followed by
etching with an acidic deoxidixer/desmutter such as SC592,
commercially available from Henkel Corporation, or other
deoxidizing solution, followed by additional rinsing prior to
anodically applied electrodeposited coating. Such pre-anodization
treatments are well known in the art.
After anodically applied electrodeposited coating, the protective
ceramic coatings produced on the surface of the workpiece are
subjected to a further treatment. The treatment may comprise
coating with a variety of coating materials including, but not
limited to paint, a thermal spray applied coating and/or a PTFE or
silicone containing paint and other suitable materials known in the
art. Thermal spray applied coating and/or a PTFE or silicone, alone
or in combination are preferred. Suitable thermal spray applied
coating compositions and thicknesses are dependent upon the
intended use of the article to be coated and are known in the
industry. By way of non-limiting example, coating materials that
can be applied by thermal spray include metals, oxides, cermets,
hard metal compounds, certain organic substances and glasses, as
well as combinations thereof, at 1-5 mils. Oxides are preferred.
Typical thickness for the thermal spray applied coating is as is
known in the art, preferably 50-100 microns, but may be 1000
microns or more. Other coating materials include PTFE or silicone
paint that may be applied to the anodized surface, with or without
an intervening layer of thermal spray applied coating, and is
typically at a film build (thickness) of from about 3 to about 30
microns to form a non-stick layer. Suitable PTFE topcoats are known
in the industry and typically comprise PTFE particles dispersed
with surfactant, solvent and other adjuvants in water. Prior art
PTFE-coated aluminiferous articles, require a primer and midcoat to
be applied prior to a topcoat containing PTFE. Primers, midcoats
and PTFE-containing topcoats, as well as silicone-containing
paints, are known in the art and providing such non-stick coatings
that are suitable for use in the invention is within the knowledge
of those skilled in the art.
Articles having the first protective coating of the invention may
be coated with PTFE coating systems known in the art, but do not
require a three-step coating process to adhere PTFE. In embodiments
having a zirconium oxide protective coating of the invention,
Applicant surprisingly found that PTFE topcoat may be applied
directly onto the zirconium oxide layer in the absence of any
intermediate coating. In a preferred embodiment, the PTFE topcoat
is applied to the zirconium oxide layer in the absence of a primer
or midcoat or both. Similarly, embodiments having a titanium oxide
protective coating of the invention, show good adhesion of the PTFE
topcoat without application of a midcoat, thus eliminating one
processing step and its attendant costs. In a preferred embodiment,
the PTFE topcoat is applied to the titanium oxide layer having a
primer thereon and in the absence of a midcoat, resulting in
non-stick coating. Applicant also discovered that a silicone
containing paint can be applied directly to zirconium and titanium
coatings of the invention with good adherence resulting in
non-stick coating.
The invention will now be further described with reference to a
number of specific examples, which are to be regarded solely as
illustrative and not as restricting the scope of the invention.
EXAMPLES
Example 1
An anodizing solution was prepared using the following
components:
TABLE-US-00003 Parts per 1000 grams Zirconium Basic Carbonate 5.24
Fluozirconic Acid (20% solution) 80.24 Deionized Water 914.5
The pH was adjusted to 3.9 using ammonia. An aluminum-containing
article was subjected to anodization for 120 seconds in the
anodizing solution using pulsed direct current having a peak
ceiling voltage of 450 volts (approximate average voltage=75
volts). The "on" time was 10 milliseconds, the "off" time was 30
milliseconds (with the "off" or baseline voltage being 0% of the
peak ceiling voltage). A uniform white coating 6.3 microns in
thickness was formed on the surface of the aluminum-containing
article. A periodic to continuous plasma (rapid flashing just
visible to the unaided human eye) was generated during anodization.
The test panels of Example 1 were analyzed using energy dispersive
spectroscopy and found to comprise a coating comprised
predominantly of zirconium and oxygen.
Example 2
An aluminum alloy article was cleaned in a diluted solution of
PARCO Cleaner 305, an alkaline cleaner, and an alkaline etch
cleaner, Aluminum Etchant 34, both commercially available from
Henkel Corporation. The aluminum alloy article was then desmutted
in SC592, an iron based acidic deoxidizer commercially available
from Henkel Corporation.
The aluminum alloy article was then coated, using the anodizing
solution of Example 1, by being subjected to anodization for 3
minutes in the anodizing solution using pulsed direct current
having a peak ceiling voltage of 500 volts (approximate average
voltage=130 volts). The "on" time was 10 milliseconds, the "off"
time was 30 milliseconds (with the "off" or baseline voltage being
0% of the peak ceiling voltage). Ceramic coatings of 3-6 microns in
thickness were formed on the surface of the aluminum alloy article.
The coatings had a uniform white appearance.
Example 3
A ceramic coated aluminum alloy article from Example 2 (said
article hereinafter referred to as Example 3) was subjected to
testing for adherence of PTFE and compared to a similar aluminum
alloy article that had been subjected to the cleaning, etching and
desmutting stages of Example 2 and then directly coated with PTFE
as described below (Comparative Example 1).
Comparative Example 1 and Example 3 were rinsed in deionized water
and dried. A standard PTFE-containing topcoat, commercially
available from Dupont under the name 852-201, was spray applied as
directed by the manufacturer. The PTFE coating on Comparative
Example 1 and Example 3 were cured at 725.degree. F. for 30 minutes
and then immersed in cold water to cool to room temperature. The
PTFE film thickness was 12-15 microns.
The films were crosshatched and subjected to adhesion tests wherein
commercially available 898 tape was firmly adhered to each film and
then pulled off at a 90.degree. angle to the surface. Comparative
Example 1 had 100% delamination of the PTFE coating in the
cross-hatch area. No loss of adhesion was observed in the PTFE
coating adhered to the ceramic-coated article from Example 3.
To assess hot/cold cycling stability, Example 3 was heated to
824.degree. F. for two hours and immediately subjected to 10
cold-water dips. The film was again cross-hatched and no
delamination of the PTFE coating was observed. The underlying
ceramic coating showed no visual changes in appearance.
Example 4
An aluminum alloy substrate in the shape of a cookware pan was the
test article for Example 4. The article was cleaned in a diluted
solution of PARCO Cleaner 305, an alkaline cleaner, and an alkaline
etch cleaner, such as Aluminum Etchant 34, both commercially
available from Henkel Corporation. The aluminum alloy article was
then desmutted in SC0592, an iron based acidic deoxidizer
commercially available from Henkel Corporation.
The aluminum alloy article was then coated, using an anodizing
solution prepared using the following components:
TABLE-US-00004 H.sub.2TiF.sub.6 12.0 g/L H.sub.3PO.sub.4 3.0
g/L
The pH was adjusted to 2.1 using ammonia. The test article was
subjected to anodization for 6 minutes in the anodizing solution
using pulsed direct current having a peak ceiling voltage of 500
volts (approximate average voltage=140 volts). The "on" time was 10
milliseconds, the "off" time was 30 milliseconds (with the "off" or
baseline voltage being 0% of the peak ceiling voltage). A uniform
blue-grey coating 10 microns in thickness was formed on the surface
of the test article. The test article was analyzed using energy
dispersive spectroscopy and found to have a coating predominantly
of titanium and oxygen, with trace amounts of phosphorus, estimated
at less than 10 wt %. The titanium dioxide ceramic-coated test
article of Example 4 was subjected to acid stability testing by
heating lemon juice (citric acid) of pH 2 and boiling to dryness in
the article. No change in the oxide layer was noted.
Example 5
An aluminum alloy test panel of 400 series aluminum alloy was
coated according to the procedure of Example 4. A scribe line was
scratched into the test panel down to bare metal prior to salt fog
testing. Despite being subjected to 1000 hours of salt fog testing
according to ASTM B-117-03, there was no corrosion extending from
the scribed line.
Example 6
An aluminum alloy wheel was the test article for Example 6. The
substrate was treated as in Example 4, except that the anodizing
treatment was as follows:
The aluminum alloy article was coated, using an anodizing solution
prepared using the following components:
TABLE-US-00005 H.sub.2TiF.sub.6 (60%) 20.0 g/L H.sub.3PO.sub.4 4.0
g/L
The pH was adjusted to 2.2 using aqueous ammonia. The article was
subjected to anodization for 3 minutes in the anodizing solution
using pulsed direct current having a peak ceiling voltage of 450
volts (approximate average voltage=130 volts) at 90.degree. F. The
"on" time was 10 milliseconds, the "off" time was 30 milliseconds
(with the "off" or baseline voltage being 0% of the peak ceiling
voltage). The average current density was 40 amps/ft2. A uniform
coating, 8 microns in thickness, was formed on the surface of the
aluminum-containing article. The article was analyzed using
qualitative energy dispersive spectroscopy and found to have a
coating predominantly of titanium, oxygen and a trace of
phosphorus.
A line was scribed into the coated article down to bare metal and
the article was subjected to the following testing: 1000 hours of
salt fog per ASTM B-117-03. The article showed no signs of
corrosion along the scribe line or along the design edges.
Example 7
An aluminum alloy test panel was treated as in Example 4. The test
panel was submerged in the anodizing solution using a titanium
alloy clamp. A uniform blue-grey coating, 7 microns in thickness,
was formed on the surface of the predominantly aluminum test panel.
A similar blue-grey coating, 7 microns, in thickness was formed on
the surface of the predominantly titanium clamp. Both the test
panel and the clamp were analyzed using qualitative energy
dispersive spectroscopy and found to have a coating predominantly
of titanium, oxygen and a trace of phosphorus.
Example 8
Aluminum alloy test panels of 6063 aluminum were treated according
to the procedure of Example 4, except that the anodizing treatment
was as follows:
The aluminum alloy articles were coated, using an anodizing
solution containing phosphorous acid in place of phosphoric
acid:
TABLE-US-00006 H.sub.2TiF.sub.6 (60%) 20.0 g/L H.sub.3PO.sub.3
(70%) 8.0 g/L
The aluminum alloy articles were subjected to anodization for 2
minutes in the anodizing solution. Panel A was subjected to 300 to
500 volts applied voltage as direct current. Panel B was subjected
to the same peak voltage but as pulsed direct current. A uniform
grey coating 5 microns in thickness was formed on the surface of
both Panel A and Panel B.
Example 9
The test article of Example 4, now having a coating of titanium
dioxide ceramic, was the subject of Example 9. Example 9 was rinsed
in deionized water and dried. The inside of the article was
overcoated with Dupont Teflon.RTM. primer and topcoat paints,
available from Dupont as 857-101 and 852-201, respectively, spray
applied as directed by the manufacturer. The primer and topcoat on
Example 9 were cured at 725.degree. F. for 30 minutes and then
immersed in cold water to cool to room temperature. The PTFE film
thickness was 5-15 microns.
Comparative Example 2 was a commercially available aluminum pan
having a non-stick seal over a hard-coat anodized coating of
aluminum oxide on the inner and outer pan surfaces.
Table 1 shows the results of repeated exposure to typical
dishwasher cycles of hot water and alkaline cleaning agents.
TABLE-US-00007 TABLE 1 Example Outside of Pan Inside of Pan
Comparative Non-stick seal removed Non-stick seal removed within
Example 2 within 6 washes and 6 washes and hardcoat is hardcoat is
attacked at attacked at surface - part is surface - part develops
covered with white white discoloration discoloration Example 9 -
Ceramic coating unaffected Teflon .RTM. coating unaffected Titanium
after 18 wash cycles after 18 wash cycles Dioxide
Example 10
For Examples 10A-D, 6063 aluminum alloy panels were cleaned in a
diluted solution of PARCO Cleaner 305, an alkaline cleaner and an
alkaline etch cleaner, such as Aluminum Etchant 34, both
commercially available from Henkel Corporation. The aluminum alloy
panels were then desmutted in SC592, an iron based acidic
deoxidizer commercially available from Henkel Corporation.
The aluminum alloy panels of Examples 10A-D were coated, using an
anodizing solution prepared using the following components:
TABLE-US-00008 H.sub.2TiF.sub.6 (60%) 20.0 g/L H.sub.3PO.sub.4
(75%) 4.0 g/L
The pH was adjusted to 2.2 using aqueous ammonia. The panels were
subjected to anodization for 3 minutes in the anodizing solution
using pulsed direct current having a peak ceiling voltage of 450
volts (approximate average voltage=130 volts) at 90.degree. F. The
"on" time was 10 milliseconds, the "off" time was 30 milliseconds
(with the "off" or baseline voltage being 0% of the peak ceiling
voltage). The average current density was 40 amps/ft2. A uniform
coating, 7.6 microns in thickness, was formed on the surface of the
aluminum-containing panels of Examples 10A-D.
For Comparative Examples 3A-D, 6063 aluminum alloy panels were
shot-blasted prior to thermal spray coating according to standard
industry practice.
Each panel of Examples 10A-D and Comparative Examples 3A-D was then
thermal spray coated using high velocity oxy-fuel (HVOF) with a
thermal spray coating as disclosed in Table 2. Each panel was
thereafter subjected to adhesion testing according to ASTM D3359
wherein the coatings were crosshatched and subjected to adhesion
tests wherein commercially available 898 tape was firmly adhered to
each film and then pulled off at a 90.degree. angle to the
surface.
TABLE-US-00009 TABLE 2 Anodically Applied Thermal Spray Test
Results from Example Electrodeposited Layer Applied Coating ASTM D
3359 Comparative 3A Shot blasted, Titania - 99 wt % TiO2 0B no
anodic oxide layer Delamination 100% loss of thermal spray applied
coating 10A Anodically Applied Titania - 99 wt % TiO2 5B
Electrodeposited TiO2 Perfect Layer Present 0% loss Comparative 3B
Shot blasted, Alumina Composite- 0B no anodic oxide layer 98.5 wt %
Al2O3; 70% loss 1.0 wt % SiO2 10B Anodically Applied Alumina
Composite- 4B Electrodeposited TiO2 98.5 wt % Al2O3; Less than 1%
loss Layer Present 1.0 wt % SiO2 Comparative 3C Shot blasted,
Zirconia Composite- 1B no anodic oxide layer 80 wt % ZrO2; 50% loss
20 wt % Y2O3 10C Anodically Applied Zirconia Composite- 4B
Electrodeposited TiO2 80 wt % ZrO2; Less than 1% loss Layer Present
20 wt % Y2O3 Comparative 3D Shot blasted, 79 wt % Fe 0B no anodic
oxide layer 18 wt % Mo 70% loss 7.0 wt % C 10D Anodically Applied
79 wt % Fe 5B Electrodeposited TiO2 18 wt % Mo Perfect Layer
Present 7.0 wt % C 0% loss
Although the invention has been described with particular reference
to specific examples, it is understood that modifications are
contemplated. Variations and additional embodiments of the
invention described herein will be apparent to those skilled in the
art without departing from the scope of the invention as defined in
the claims to follow. The scope of the invention is limited only by
the breadth of the appended claims.
* * * * *